Dew Sprinkler Service Inc

We have used Dew Sprinkler for 3 years now. They installed our sprinkler system, and have done the winterization and spring startup since we installed it. This year they said that a valve stem is broken and needed to be replaced, however they are the only ones that touch the valve stem (the whole system for that matter). They refuse to acknowledge that it was their fault, instead the owner of the company kept suggesting various scenarios for how else the valve stem broke (eg. someone stepped on it, a lawn mower hit it, painters dropped something on it, some one else worked on it). None of these scenarios are not possible. Now they want to charge me to replace this valve, without which my sprinkler system wont work. Needless to say, I will be finding someone else to do this for me. Please safe yourself the hassle, and find someone else for your sprinkler needs!